In an era of rising power use and costs, efficiency is job one. The issue: What's the best way to cool your data center, plug holes and minimize your footprint.

Data center managers are on the hot seat lately. They not only have to cram in more servers per square inch than they ever wanted or thought they'd need, they also have to figure out how to do it without sending the electricity bill through the roof.

And they're not entirely sure how to do it.

Traditionally, they've had to worry only about getting as much power in as possible, not about making sure they used it efficiently.

"When it comes to data centers, cost isn't irrelevant, but it's not about cost. It's about uptime," said Rick Oliver, data center operations senior engineer at the University of Phoenix, a for-profit online university based in Phoenix.

So, as companies have built new facilities, it's been more important to overbuild than underbudget. That has meant adding in as many air conditioning and other environmental controls as they practically could and talking the local utility company into running in as many redundant power lines as they ever expected to need.

"You go in thinking about the future, about the systems we're going to have, and about heating and cooling them, in three years or five years," said Seth Mitchell, infrastructure team manager for Slumberland, a furniture retailer based in Little Canada, Minn.

"You have to extrapolate where you're going to be because building a [data center] room is a fairly permanent thing. It's not easy to make changes to a permanent design."

Not that Mitchell has much of a choice. Escalating energy costs, which seem to rise with every new conflict in the Mideast or with every Alaskan oil pipeline problem, are causing customers and technology vendors to rethink the data center.

On Aug. 16, engineers at the Lawrence Berkeley National Laboratory and about 20 technology vendors concluded a demonstration of DC power in a data center.

Hewlett-Packard is looking to nature to redesign the data center of the future, and suppliers ranging from Advanced Micro Devices to Intel to Sun Microsystems are trying to cut power costs.

"The people who spec and build the data centers are not the ones who pay the electric bill," said Neil Rasmussen, chief technology officer and co-founder of American Power Conversion, in West Kingston, R.I. "Many of them didn't know what it was or even who paid it."

As a result, data center managers are doubling as HVAC (heating, ventilating and air conditioning) experts as well as certified IT administrators.

In their efforts to "green" the data center, they are learning to unlearn a lot of data center architecture design that has been handed down over the years.

Any data center, but especially one crammed with servers stacked in compact chassis, is "a radical consumption of power, and the exhaust of power is heat; there is no way you can consume one without the other," Oliver said.

But as the typical server unit has shrunk from a stand-alone pedestal the size of a filing cabinet to 2U (3.5-inch) stackables, 1U (1.75-inch) pizza boxes and even blades, both power and heat cause problems.

"The whole industry has gotten hotter and more power-hungry. Within the last five years, servers went from using around 30 watts per processor to now more like 135 watts per processor," Oliver said. "You used to be able to put in up to six servers per rack; now it's up to 42."